diff --git a/internal/translator/antigravity/claude/antigravity_claude_response.go b/internal/translator/antigravity/claude/antigravity_claude_response.go
index 52fc358e..d26a1c9f 100644
--- a/internal/translator/antigravity/claude/antigravity_claude_response.go
+++ b/internal/translator/antigravity/claude/antigravity_claude_response.go
@@ -9,11 +9,16 @@ package claude
 import (
 	"bytes"
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"fmt"
 	"strings"
 	"sync/atomic"
 	"time"
 
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/cache"
+	log "github.com/sirupsen/logrus"
+
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
 )
@@ -35,6 +40,31 @@ type Params struct {
 	HasSentFinalEvents   bool   // Indicates if final content/message events have been sent
 	HasToolUse           bool   // Indicates if tool use was observed in the stream
 	HasContent           bool   // Tracks whether any content (text, thinking, or tool use) has been output
+
+	// P3: Signature caching support
+	SessionID           string          // Session ID derived from request for signature caching
+	CurrentThinkingText strings.Builder // Accumulates thinking text for signature caching
+}
+
+// deriveSessionIDFromRequest generates a stable session ID from the request JSON.
+func deriveSessionIDFromRequest(rawJSON []byte) string {
+	messages := gjson.GetBytes(rawJSON, "messages")
+	if !messages.IsArray() {
+		return ""
+	}
+	for _, msg := range messages.Array() {
+		if msg.Get("role").String() == "user" {
+			content := msg.Get("content").String()
+			if content == "" {
+				content = msg.Get("content.0.text").String()
+			}
+			if content != "" {
+				h := sha256.Sum256([]byte(content))
+				return hex.EncodeToString(h[:16])
+			}
+		}
+	}
+	return ""
 }
 
 // toolUseIDCounter provides a process-wide unique counter for tool use identifiers.
@@ -62,6 +92,7 @@ func ConvertAntigravityResponseToClaude(_ context.Context, _ string, originalReq
 			HasFirstResponse: false,
 			ResponseType:     0,
 			ResponseIndex:    0,
+			SessionID:        deriveSessionIDFromRequest(originalRequestRawJSON),
 		}
 	}
 
@@ -119,11 +150,20 @@ func ConvertAntigravityResponseToClaude(_ context.Context, _ string, originalReq
 				// Process thinking content (internal reasoning)
 				if partResult.Get("thought").Bool() {
 					if thoughtSignature := partResult.Get("thoughtSignature"); thoughtSignature.Exists() && thoughtSignature.String() != "" {
+						log.Debug("Branch: signature_delta")
+
+						if params.SessionID != "" && params.CurrentThinkingText.Len() > 0 {
+							cache.CacheSignature(params.SessionID, params.CurrentThinkingText.String(), thoughtSignature.String())
+							log.Debugf("Cached signature for thinking block (sessionID=%s, textLen=%d)", params.SessionID, params.CurrentThinkingText.Len())
+							params.CurrentThinkingText.Reset()
+						}
+
 						output = output + "event: content_block_delta\n"
 						data, _ := sjson.Set(fmt.Sprintf(`{"type":"content_block_delta","index":%d,"delta":{"type":"signature_delta","signature":""}}`, params.ResponseIndex), "delta.signature", thoughtSignature.String())
 						output = output + fmt.Sprintf("data: %s\n\n\n", data)
 						params.HasContent = true
 					} else if params.ResponseType == 2 { // Continue existing thinking block if already in thinking state
+						params.CurrentThinkingText.WriteString(partTextResult.String())
 						output = output + "event: content_block_delta\n"
 						data, _ := sjson.Set(fmt.Sprintf(`{"type":"content_block_delta","index":%d,"delta":{"type":"thinking_delta","thinking":""}}`, params.ResponseIndex), "delta.thinking", partTextResult.String())
 						output = output + fmt.Sprintf("data: %s\n\n\n", data)
@@ -152,6 +192,9 @@ func ConvertAntigravityResponseToClaude(_ context.Context, _ string, originalReq
 						output = output + fmt.Sprintf("data: %s\n\n\n", data)
 						params.ResponseType = 2 // Set state to thinking
 						params.HasContent = true
+						// P3: Start accumulating thinking text for signature caching
+						params.CurrentThinkingText.Reset()
+						params.CurrentThinkingText.WriteString(partTextResult.String())
 					}
 				} else {
 					finishReasonResult := gjson.GetBytes(rawJSON, "response.candidates.0.finishReason")
diff --git a/internal/translator/antigravity/claude/antigravity_claude_response_test.go b/internal/translator/antigravity/claude/antigravity_claude_response_test.go
new file mode 100644
index 00000000..7ffd7666
--- /dev/null
+++ b/internal/translator/antigravity/claude/antigravity_claude_response_test.go
@@ -0,0 +1,389 @@
+package claude
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/cache"
+)
+
+func TestConvertBashCommandToCmdField(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "basic command to cmd conversion",
+			input:    `{"command": "git diff"}`,
+			expected: `{"cmd":"git diff"}`,
+		},
+		{
+			name:     "already has cmd field - no change",
+			input:    `{"cmd": "git diff"}`,
+			expected: `{"cmd": "git diff"}`,
+		},
+		{
+			name:     "both cmd and command - keep cmd only",
+			input:    `{"command": "git diff", "cmd": "ls"}`,
+			expected: `{"command": "git diff", "cmd": "ls"}`, // no change when cmd exists
+		},
+		{
+			name:     "command with special characters in value",
+			input:    `{"command": "echo \"command\": test"}`,
+			expected: `{"cmd":"echo \"command\": test"}`,
+		},
+		{
+			name:     "command with nested quotes",
+			input:    `{"command": "bash -c 'echo \"hello\"'"}`,
+			expected: `{"cmd":"bash -c 'echo \"hello\"'"}`,
+		},
+		{
+			name:     "command with newlines",
+			input:    `{"command": "echo hello\necho world"}`,
+			expected: `{"cmd":"echo hello\necho world"}`,
+		},
+		{
+			name:     "empty command value",
+			input:    `{"command": ""}`,
+			expected: `{"cmd":""}`,
+		},
+		{
+			name:     "command with other fields - preserves them",
+			input:    `{"command": "git diff", "timeout": 30}`,
+			expected: `{ "timeout": 30,"cmd":"git diff"}`,
+		},
+		{
+			name:     "invalid JSON - returns unchanged",
+			input:    `{invalid json`,
+			expected: `{invalid json`,
+		},
+		{
+			name:     "empty object",
+			input:    `{}`,
+			expected: `{}`,
+		},
+		{
+			name:     "no command field",
+			input:    `{"restart": true}`,
+			expected: `{"restart": true}`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := convertBashCommandToCmdField(tt.input)
+			if result != tt.expected {
+				t.Errorf("convertBashCommandToCmdField(%q) = %q, want %q", tt.input, result, tt.expected)
+			}
+		})
+	}
+}
+
+// ============================================================================
+// P3: Signature Caching Tests
+// ============================================================================
+
+func TestConvertAntigravityResponseToClaude_SessionIDDerived(t *testing.T) {
+	cache.ClearSignatureCache("")
+
+	// Request with user message - should derive session ID
+	requestJSON := []byte(`{
+		"messages": [
+			{"role": "user", "content": [{"type": "text", "text": "Hello world"}]}
+		]
+	}`)
+
+	// First response chunk with thinking
+	responseJSON := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": "Let me think...", "thought": true}]
+				}
+			}]
+		}
+	}`)
+
+	var param any
+	ctx := context.Background()
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, responseJSON, &param)
+
+	// Verify session ID was set
+	params := param.(*Params)
+	if params.SessionID == "" {
+		t.Error("SessionID should be derived from request")
+	}
+}
+
+func TestConvertAntigravityResponseToClaude_ThinkingTextAccumulated(t *testing.T) {
+	cache.ClearSignatureCache("")
+
+	requestJSON := []byte(`{
+		"messages": [{"role": "user", "content": [{"type": "text", "text": "Test"}]}]
+	}`)
+
+	// First thinking chunk
+	chunk1 := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": "First part of thinking...", "thought": true}]
+				}
+			}]
+		}
+	}`)
+
+	// Second thinking chunk (continuation)
+	chunk2 := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": " Second part of thinking...", "thought": true}]
+				}
+			}]
+		}
+	}`)
+
+	var param any
+	ctx := context.Background()
+
+	// Process first chunk - starts new thinking block
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, chunk1, &param)
+	params := param.(*Params)
+
+	if params.CurrentThinkingText.Len() == 0 {
+		t.Error("Thinking text should be accumulated after first chunk")
+	}
+
+	// Process second chunk - continues thinking block
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, chunk2, &param)
+
+	text := params.CurrentThinkingText.String()
+	if !strings.Contains(text, "First part") || !strings.Contains(text, "Second part") {
+		t.Errorf("Thinking text should accumulate both parts, got: %s", text)
+	}
+}
+
+func TestConvertAntigravityResponseToClaude_SignatureCached(t *testing.T) {
+	cache.ClearSignatureCache("")
+
+	requestJSON := []byte(`{
+		"messages": [{"role": "user", "content": [{"type": "text", "text": "Cache test"}]}]
+	}`)
+
+	// Thinking chunk
+	thinkingChunk := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": "My thinking process here", "thought": true}]
+				}
+			}]
+		}
+	}`)
+
+	// Signature chunk
+	validSignature := "abc123validSignature1234567890123456789012345678901234567890"
+	signatureChunk := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": "", "thought": true, "thoughtSignature": "` + validSignature + `"}]
+				}
+			}]
+		}
+	}`)
+
+	var param any
+	ctx := context.Background()
+
+	// Process thinking chunk
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, thinkingChunk, &param)
+	params := param.(*Params)
+	sessionID := params.SessionID
+	thinkingText := params.CurrentThinkingText.String()
+
+	if sessionID == "" {
+		t.Fatal("SessionID should be set")
+	}
+	if thinkingText == "" {
+		t.Fatal("Thinking text should be accumulated")
+	}
+
+	// Process signature chunk - should cache the signature
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, signatureChunk, &param)
+
+	// Verify signature was cached
+	cachedSig := cache.GetCachedSignature(sessionID, thinkingText)
+	if cachedSig != validSignature {
+		t.Errorf("Expected cached signature '%s', got '%s'", validSignature, cachedSig)
+	}
+
+	// Verify thinking text was reset after caching
+	if params.CurrentThinkingText.Len() != 0 {
+		t.Error("Thinking text should be reset after signature is cached")
+	}
+}
+
+func TestConvertAntigravityResponseToClaude_MultipleThinkingBlocks(t *testing.T) {
+	cache.ClearSignatureCache("")
+
+	requestJSON := []byte(`{
+		"messages": [{"role": "user", "content": [{"type": "text", "text": "Multi block test"}]}]
+	}`)
+
+	validSig1 := "signature1_12345678901234567890123456789012345678901234567"
+	validSig2 := "signature2_12345678901234567890123456789012345678901234567"
+
+	// First thinking block with signature
+	block1Thinking := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": "First thinking block", "thought": true}]
+				}
+			}]
+		}
+	}`)
+	block1Sig := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": "", "thought": true, "thoughtSignature": "` + validSig1 + `"}]
+				}
+			}]
+		}
+	}`)
+
+	// Text content (breaks thinking)
+	textBlock := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": "Regular text output"}]
+				}
+			}]
+		}
+	}`)
+
+	// Second thinking block with signature
+	block2Thinking := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": "Second thinking block", "thought": true}]
+				}
+			}]
+		}
+	}`)
+	block2Sig := []byte(`{
+		"response": {
+			"candidates": [{
+				"content": {
+					"parts": [{"text": "", "thought": true, "thoughtSignature": "` + validSig2 + `"}]
+				}
+			}]
+		}
+	}`)
+
+	var param any
+	ctx := context.Background()
+
+	// Process first thinking block
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, block1Thinking, &param)
+	params := param.(*Params)
+	sessionID := params.SessionID
+	firstThinkingText := params.CurrentThinkingText.String()
+
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, block1Sig, &param)
+
+	// Verify first signature cached
+	if cache.GetCachedSignature(sessionID, firstThinkingText) != validSig1 {
+		t.Error("First thinking block signature should be cached")
+	}
+
+	// Process text (transitions out of thinking)
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, textBlock, &param)
+
+	// Process second thinking block
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, block2Thinking, &param)
+	secondThinkingText := params.CurrentThinkingText.String()
+
+	ConvertAntigravityResponseToClaude(ctx, "claude-sonnet-4-5-thinking", requestJSON, requestJSON, block2Sig, &param)
+
+	// Verify second signature cached
+	if cache.GetCachedSignature(sessionID, secondThinkingText) != validSig2 {
+		t.Error("Second thinking block signature should be cached")
+	}
+}
+
+func TestDeriveSessionIDFromRequest(t *testing.T) {
+	tests := []struct {
+		name      string
+		input     []byte
+		wantEmpty bool
+	}{
+		{
+			name:      "valid user message",
+			input:     []byte(`{"messages": [{"role": "user", "content": "Hello"}]}`),
+			wantEmpty: false,
+		},
+		{
+			name:      "user message with content array",
+			input:     []byte(`{"messages": [{"role": "user", "content": [{"type": "text", "text": "Hello"}]}]}`),
+			wantEmpty: false,
+		},
+		{
+			name:      "no user message",
+			input:     []byte(`{"messages": [{"role": "assistant", "content": "Hi"}]}`),
+			wantEmpty: true,
+		},
+		{
+			name:      "empty messages",
+			input:     []byte(`{"messages": []}`),
+			wantEmpty: true,
+		},
+		{
+			name:      "no messages field",
+			input:     []byte(`{}`),
+			wantEmpty: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := deriveSessionIDFromRequest(tt.input)
+			if tt.wantEmpty && result != "" {
+				t.Errorf("Expected empty session ID, got '%s'", result)
+			}
+			if !tt.wantEmpty && result == "" {
+				t.Error("Expected non-empty session ID")
+			}
+		})
+	}
+}
+
+func TestDeriveSessionIDFromRequest_Deterministic(t *testing.T) {
+	input := []byte(`{"messages": [{"role": "user", "content": "Same message"}]}`)
+
+	id1 := deriveSessionIDFromRequest(input)
+	id2 := deriveSessionIDFromRequest(input)
+
+	if id1 != id2 {
+		t.Errorf("Session ID should be deterministic: '%s' != '%s'", id1, id2)
+	}
+}
+
+func TestDeriveSessionIDFromRequest_DifferentMessages(t *testing.T) {
+	input1 := []byte(`{"messages": [{"role": "user", "content": "Message A"}]}`)
+	input2 := []byte(`{"messages": [{"role": "user", "content": "Message B"}]}`)
+
+	id1 := deriveSessionIDFromRequest(input1)
+	id2 := deriveSessionIDFromRequest(input2)
+
+	if id1 == id2 {
+		t.Error("Different messages should produce different session IDs")
+	}
+}